About 50% of children and adolescents with intellectual disability have a mental disorder or serious behavior problems; this is three times as high as is found in typically developing youth. This dual diagnosis (intellectual disability and mental disorder) puts them at much heightened risk for a host of unfavorable long- term life outcomes. Too, these youth present major coping and health challenges to their families and also economic challenges to the service delivery system. While there are certainly some syndrome-related contributions to dual diagnosis, most children with mild or borderline intellectual disability do not have identified genetic syndromes. There have been dramatic advances in developmental psychopathology in addressing the basic questions of continuity of mental disorder across childhood, and the mechanisms by which risk and protective factors have an influence. Unfortunately, youth with intellectual disability are routinely excluded from most studies, so there has been little advance in our understanding of prevention of dual diagnosis. This is a proposal to continue the Collaborative Family Study, a unique longitudinal prospective study that focuses on the development of psychopathology and social competence in youth with intellectual disability; there is also a contrasting group of typically developing youth. The primary aim is to determine the emergence and continuity of psychopathology from early childhood through adolescence, and to understand the dynamic influences of early and ongoing family processes, as well as school experiences, on regulatory capacities and outcomes for children with and without intellectual disability. The CFS has assessed 190 children and their families annually from child age 3 to 9 years, obtaining in- depth child developmental assessments, naturalistic and structured observations of parent-child interactions and children's emotional and behavioral regulation, comprehensive reports of parent and child functioning, and assessments from the children's schools. Findings to date indicate that early family processes do relate to the child's self-regulatory abilities and child subsequent challenging behaviors, which, in turn, increase stress and impair mental and physical health in the child's family. We propose continuing the CFS through early adolescence (ages 12 13, 15), when risk for many mental disorders increases. We will recruit an additional sample (n=90) that will be at least 60% Hispanic, and study the relationships between family processes and youths' psychopathology and social competence within two prominent cultural groups (Hispanics and non- Hispanic Whites). This study has direct public health relevance, given the enormity of the problem of mental disorder in intellectual disability. Findings about the course and causes of psychopathology in these youth could inform prevention and early intervention programs, as well as parent education programs through adolescence, school curricula, and therapeutic programs for the youth themselves. PUBLIC HEALTH RELEVANCE: Children with intellectual disability (mental retardation) are about three times as likely to have mental disorders or serious behavior problems as are typically developing children, but little is known about causes. This prospective longitudinal study, from child age 3 to 15 years, is assessing child, family, school, and cultural influences on the development of psychopathology and social competence in children and adolescents with intellectual disability and a typically developing comparison group. It has direct public health relevance, as findings about the course and causes of psychopathology in these youth could inform the content of prevention and early intervention programs, as well as parent education programs, school curricula, and therapeutic programs for the youth themselves.